GEDV: Global End-diastolic Volume

GEDV is the difference between the ITTV and PTV

The Pulmonary Thermal Volume (PTV) can be subtracted from the IntraThoracic Thermal Volume (ITTV).


MTt (Mean Transit Time) multiplied by cardiac output(CO) determines your ITTV (intrathoracic thermal volume)
The other time parameter is your Down Slope Time (DSt)

GEDV diagram

Remembering that ITTV and PTV are derived from MTt and Dst,

GEDV equation

GEDV is a poor predictor of fluid responsiveness.

GEDV relates well to preload, but somehow not to fluid responsiveness.

In his 2009 review, Marik et al trashed GEDVI as a means of predicting fluid response - it was no better than CVP or PAWP, which is to say "next to useless". Additionally, GEDV loses its correlation with preload in early sepsis.

So, in short, GEDV and GEDVI should not be used to guide volume resuscitation. The details of how this heavily marked static parameter became popular are discussed in a dedicated chapter in the Fluid Resuscitation section.

References

From Bersten and Soni’s” Oh's Intensive Care Manual”, 6th Edition, as well as http://www.pulsion.com/ who are sadly the best source for this sort of information.

Endo, Tomoyuki, et al. "Limitations of global end-diastolic volume index as a parameter of cardiac preload in the early phase of severe sepsis: a subgroup analysis of a multicenter, prospective observational study." Journal of Intensive Care 1.1 (2013): 1-8.'

Marik, Paul E., et al. "Dynamic changes in arterial waveform derived variables and fluid responsiveness in mechanically ventilated patients: a systematic review of the literature*." Critical care medicine 37.9 (2009): 2642-2647.